The present invention relates generally to hydraulic systems driven by internal combustion engines and more particularly to a bypass valve which bypasses hydraulic fluid from the outlet to the inlet of a hydraulic pump at engine cranking speed and then blocks the bypass at low engine idle speed.
In the past, internal combustion engines which drove hydraulic systems required large electrical starting motors capable of turning over the engines while driving the pumps and pump-associated fluid functions. While numerous ways of disengaging the hydraulic system have been tried, they have always had the disadvantage of being complex or expensive or both.
None of the systems heretofore devised has been able to cause the pump to operate at all temperatures at no load by bypassing fluid from the pump outlet to its inlet when the flow rate is around the rate developed at engine cranking speed and blocking the bypass when the flow rate is at the rate developed at low engine idle speed. One of the major problems has been in dealing with the temperature induced viscosity changes in the system's hydraulic fluid which make a device developed for low temperatures unsuitable for high temperatures and vice versa.